Problem: Expand.
Explanation: $\begin{aligned} ( x{-7})(x-3)&= x(x-3){-7}(x-3) \end{aligned}$ $\begin{aligned} \phantom{( x{-7})(x-3)}&=x^2-3x-7x+21 \\\\ &=x^2-10x+21 \end{aligned}$